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Fix: curly `multi` reports single lexical declarations (fixes #11908) #12513

merged 1 commit into from Nov 4, 2019


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mdjermanovic commented Oct 30, 2019

What is the purpose of this pull request? (put an "X" next to item)

[X] Bug fix #11908

Tell us about your environment

  • ESLint Version: 6.6.0
  • Node Version: 10.16.0
  • npm Version: 6.9.0

What parser (default, Babel-ESLint, etc.) are you using?


Please show your full configuration:

module.exports = {
    parserOptions: {
		ecmaVersion: 2015,

What did you do? Please include the actual source code causing the issue.

Online Demo Link

/* eslint curly: ["error", "multi"] */

if (foo) {
    const a = 1;

What did you expect to happen?

0 errors. A block with only one statement which is a lexical declaration doesn't make much sense, but still these curly braces cannot be removed.

What actually happened? Please include the actual, raw output from ESLint.

1 error and syntax error in the fixed code.

3:1  error  Unnecessary { after 'if' condition  curly
/* eslint curly: ["error", "multi"] */

if (foo) 
    const a = 1;
4:2  error  Parsing error: Unexpected token const

What changes did you make? (Give an overview)

Changed the multi option to not report single-statement blocks if that statement is a let, const, function or class declaration.

Is there anything you'd like reviewers to focus on?

The following added valid test were invalid, and the autofix was producing syntax errors:

if (foo) { const bar = 'baz'; }
while (foo) { let bar = 'baz'; }
for (foo in bar) { class Baz {} }

The same applies to these valid tests with the consistent modifier:

if (foo) { let bar; } else { baz(); }
if (foo) { bar(); } else { const baz = 'quux'; }

The following valid test was also invalid. This code without braces is not a syntax error in non-strict mode, but it's a legacy syntax, so the original code shouldn't be reported and auto-fixed:

for(;;) { function foo() {} }

This invalid test was invalid before, it's a regression test:

if (foo) { var bar = 'baz'; }

These two invalid tests with the consistent modifier were invalid before, but in a different way. Autofix was removing braces, which was producing syntax errors. After this PR, autofix will do the opposite, put the braces around the statement that isn't in a block.

if (foo) { let bar; } else baz();
if (foo) bar(); else { const baz = 'quux' }

That's the only case where this PR can produce more warnings (e.g. 2 instead of 1), but that can happen only in chains that already have warnings.

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kaicataldo left a comment

LGTM, thanks!

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mysticatea left a comment

LGTM, thank you very much!

@kaicataldo kaicataldo merged commit bb556d5 into master Nov 4, 2019
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@kaicataldo kaicataldo deleted the issue11908 branch Nov 4, 2019
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kaicataldo commented Nov 4, 2019

Thanks for contributing!

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